Chromatographic processes are known in the art. They provide a means of separating and analyzing mixtures of solutions by selective adsorption on materials such as nylon, alumina, and silica. The process is based on differences in the distribution ratios of the components of mixtures between a mutually immiscible mobile and a fixed stationary phase. In particular, there are formed isolated spots or bands which can be separated mechanically and further examined. In thin layer chromatography, it is known to use thin films, such as silica mixed with a binder (e.g. calcium sulfate) adhered to glass for the separating vehicle.
U.S. Pat. No. 4,153,661 discloses a method of making a polytetrafluoroethylene composite sheet comprising a PTFE matrix with particulate material, which is substantially insoluble in water, dispersed therein. The resulting sheet is extremely pliable, akin to doe skin. It is said to be useful as an electronic insulator or a semipermeable membrane.
U.S. Pat. No. 4,373,519 discloses a composite wound dressing comprising a PTFE matrix with water-swellable hydrophilic absorptive particles enmeshed in the matrix, and, optionally, a partially occlusive film coated on one surface of the matrix. It is disclosed that the particulate material can account for from 40 to 90% by weight of the total composition, of which up to 50% can be inert property modifier particles. Examples of property modifier particles include silica, kaolin, talc, bentonite, vermiculite, etc. The sheets are described as conformable and chamois-like.
U.S. Pat. Nos. 4,565,663 and 4,460,642, which are related to U.S. Pat. No. 4,373,519 (a division of a continuation-in-part application and a continuation-in-part, respectively) disclose water-swellable composite sheets having a PTFE matrix in which water-swellable hydrophilic absorptive particles are enmeshed. As in U.S. Pat. No. 4,373,519 the water-swellable particulate can account for from 40 to 90% by weight of the total composition, of which up to 50% by weight can be inert property modifier particles, e.g. silica. The sheets are described as conformable and chamois-like. It is disclosed that they can be used as chromatographic materials. It is also disclosed that certain water-swellable cation exchange resins can be used as particulate in chromatographic supports.